This invention relates to an adaptive arrangement for the identification of a periodic signal comprising an evaluation circuit for digitizing the signal and for detecting its extreme value, as well as subsequent means for detecting the fundamental oscillation of the signal.
Arrangements of this type are used to identify periodic signals having an unkown frequency, amplitude and offset position, as well as dips in the amplitude in the region of its extreme value. These parameters of the signal to be identified, abbreviated to signal hereinafter, are furthermore also subjected to variations in time. Examples of signals of this type are signals from speed sensors which are used in, for example, anti-locking systems, anti-slip systems etc. Speed sensors of this type usually produce a relatively small, fluctuating sensor signal on which a d.c. voltage is superposed. Via a subsequent comparator this changing sensor signal, beset with fluctuations, is usually digitized, that is to say it is converted into a corresponding square-wave signal and applied to a further evaluation circuit.
Identification or measuring arrangements of this type are known. They usually have a gear wheel whose signal indicates the number of revolutions and is sampled via, for example, a magnetically operating speed sensor. The German Patent Application P 3926617.6, which corresponds to U.S. Application Ser. No. 562,526, filed Aug. 3, 1990, corresponding arrangement which comprises means for amplifying, comparing and evaluating the sensor signal of the speed sensor to produce a corresponding digital output signal. In accordance with said arrangement, the signal must be unambiguously identified and evaluated, for which purpose a window comparator having a controllable window is provided as a comparator means which, via at least one logic circuit member drives a flip-flop for the supply of the output signal and is followed by means which, in dependence on the offset position continuously produce corresponding reference signals for the window comparator. The comparator and evaluation devices of this prior art arrangement furthermore include an oscillator for adapting the window range to the signal to be identified. For the case in which the signal has a dip in the regions of its peak value, there is provided in accordance with this prior art arrangement an oscillator frequency which is not significantly greater than the frequency of the signal so that the window of the window comparator does not track the signal anymore, but tracks it with some delay, the degree of this delay being limited by the oscillator frequency. At low frequencies of the signal the signal is also tracked in the region of the dips so that, as regards dips in the signal to be identified in the region of its extreme values, this prior art arrangement is not entirely reliable.